1. Technical Field
The present invention relates to a punch drive apparatus equipped in a punching press machine.
2. Background Art
In a conventional mechanical punch press machine as a punch drive apparatus which produces up and down motion of a ram, a crank drive apparatus has been used wherein the bottom end of a pitman arm connected with the crank shaft is engaged with a ram. In this mechanism, one rotation of the crank shaft generates one up and down motion of the ram. Therefore rotational velocity of the crank shaft must be increased in order to reduce processing time by high-speed punching. However, increasing punching speed is not easy to achieve because the rotational velocity of the crank shaft is limited according to the rotational velocity of the motor or the characteristics of a shaft bearing. Even if increasing the rotation velocity of the crank shaft is possible, that approach would increase the noise during the punching operation. Further, since the crank moves fastest at the midpoint of the up-down stroke and slowest near the top and bottom dead points in the crank drive apparatus described above, the stroke velocity near the bottom dead point after the punching tool actually hits a workpiece is slow, causing difficulty in achieving an adequate stroke velocity according to the material and thickness of the workpiece.